A system for preparing a liquid coffee extract of relatively small volume such as ristretto, espresso or lungo, from a single-use capsule containing roast and ground coffee powder in a high-pressure extraction apparatus is known.
One of the most successful coffee capsule system (e.g., Nespresso® coffee system) and commercialized for many years, comprises a single-use coffee capsule with a tearable extraction foil member, a cup-shaped body comprising a cavity containing a predetermined amount of roast and ground coffee and closed by the foil member.
For the preparation of the coffee extract, the capsule is received in an extraction chamber of the apparatus. The chamber is generally formed by the arrangement of a water injection cage and an extraction plate closing about the capsule. The perforation of outlet orifices for draining the coffee extract from the capsule is, in certain non-limiting embodiments, obtained under the effect of the pressure of liquid which is injected inside the capsule for pressing and tearing or stretching the foil member against the tearing portion of the extraction plate. For this, the capsule extraction plate comprises truncated pyramids (in relief) and a network of flow channels (in recess). The capsule has a thin, flexible foil member (hereafter referred as “tearable foil member”) such as aluminium which tears or stretch under a pressure of several bar and at a plurality of locations, in particular along the edges of the truncated pyramids, forming small filtering orifices for the coffee extract to flow through. The coffee extract is further drained via small holes provided in the flow channels and through the extraction plate.
The existing coffee capsules have generally a volume adapted for containing a limited amount of coffee but suitable for producing under pressure short coffee extracts within a wide range of intensity and different sensory (flavour or aromatic) profiles. Many different coffee related factors can potentially vary the intensity and/or flavour of the coffee extract, in particular, the coffee weight, the granulometry (grind size, size distribution, percentage of fine particles), bean roasting degree, compaction, coffee origin, coffee blends. Also, many system related factors may also influence the intensity and flavour of the coffee extract such as the correlated parameters of pressure/flow rate, the water volume, etc.
In the small available volume of the existing capsule used in the coffee high-pressure apparatus, the weight of coffee it may contain cannot exceed 6.5 grams. Above this limit, the coffee powder becomes too compacted and this may create preferential path for liquid and/or blocking. As a result, the coffee extraction is not optimal and/or the liquid coffee flow can be too slow and is often blocked before the end of the coffee extraction.
Also, with a higher weight of coffee powder for preparing a relatively short coffee, more undesired coffee compounds can be extracted and/or off-flavour notes can be generated.
Therefore, there is a need for providing more intense and/or more aromatically complex coffee extracts using the extraction principle known while limiting extraction of undesired coffee compounds and/or generating off-flavour notes.